[pkg-go] Bug#948565: (no subject)

[Daniel Swarbrick]

I tracked the problem down to the fact that the http.ResponseWriter is 
being wrapped by github.com/opentracing-contrib/go-stdlib, causing the 
Flusher() method to be masked. As a result, the ResponseWriter does not 
satisfy the http.Flusher interface.

I have tested building with a newer version of 
opentracing-contrib/go-stdlib (currently pending review by the package 
maintainer) and it resolves the issue.

Once the updated golang-github-opentracing-contrib-go-stdlib package is 
approved and uploaded, we can build a new prometheus package against it.